Is your backup in a safe location?
Do you keep your backup in the same place as the original files? If there is a fire that destroys your house or building, is your backup safe?
Backups that are stored in the same place as the original files are not safe. Even if there is no theft, flooding or fire, you could loose your backups.
Climate conditions, like relative air humidity and temperature can affect electronic equipment.
It's not rare that an external backup hard drive fails and that there is a fail on the internal hard drive on a small time length span.
You will only be aware you lost your files, when your computer stops working and there is nothing to be done.
You must have at least one backup in a safe location.